Magnetic core for coils and the like



Dec. 15, 1931.

S. BECKINSALE ET AL- MAGNETIC CORE FOR COILS AND THE LIKE Filed July 17,1931 INVENTORS fiM ti; mew/M ATTORNEYS Patented Dec. 15, 1931 I D A E NTOrr-105* SYDNEY AND HAROLD JOHN .ALTJCOCK, BELVEDERE, 'xmmnnemnn men'mroe931: roa corns m m Lima Application filed July 17, 1931, Sam-131 80.551,376, and in GreatBritain- July 85,1880.

This invention relates to cores made from powdered magnetic material.Such cores are chiefly used for loading coils for telephone lines andfor transformers for currents of audible frequencies. In-s'uch cores ithas been recognized as desirable to separate from each otherelectrically the particles of magnetic material. This has been done bycoating the magnetic particles or by m mixing .them with particles ofother materials, frequently using abinder to hold the mixture or coatedparticles together.

In accordance with the present invention we utilize as the separatingmaterial magne- 15, sium hydroxide which may be applied either as acoating or as particles mixed with the magnetic particles. In eithercase the hydroxide is obtained by applying magnesium to the magneticmaterial and treating the n magnesium after application with steam at anappropriate temperature and pressure to convert it into hydroxide. I

- In producing a coating on the finely divided magnetic material this ispassed through a region into which magnesium is introduced in avapourized condition, for instance, by spraying. The magnesium isdeposited as a thin coating on the iron and may be subsequentlyconverted to magnesium hydroxide while adhering to the iron.

When applying the separating material as a mixture the magnesium ispowdered to a definitely greater fineness than the magnetic material sothat when the mixture is made up'the magnesium will coat the iron.

The steam heat treatment may be carried out eitherbefore or aftercompression of the powder to form the core. This treatment consists incooking the magnetic material with the magnesium in a steam atmosphereat raised temperature and pressure. The actual temperature and pressuredepend upon the amount of magnesium present and upon other matters suchas the shape and dimensions of the core when treatment is given aftermoulding. Pressures of between thirty and eighty pounds per square inchabove atmosphere with temperatures of from 250 to 800 F. have been foundto be suitan ble. Treatment before moulding is advantageous for severalreasons. It permits the agitation of the powder which may be employed tofacilitate the action. If treatment is carried out after moulding it maybe desirable to provide against the disadvantageous results of thesllght increase in volume which takes place in changing from magnesiumto magnesium hydroxide. This may be taken care of by placing thecores inclose fitting containers during heat treatment, provision being made ofcourse for the entry of the steam into the containers.

The accompanying diagrammatic drawings show two pieces of apparatuswhich may be used for the coating processes.

Figure 1 shows in section a rotary apparatus, and

Figure 2 shows in section a stationary apparatus.

In using the'method of coating with vapourized magnesium we prefer tospray this into a chamber in whichthe iron 'or iron alloy dust is keptin a state of violent agitation. This may be a rotating rumbler 1(Figure 1) or a chamber 2 (Figure 2) into which the iron or iron alloydust is blown by a jet 3 in a stream against which the jet 4 causes astream of magnesium vapour to impinge. 7

With the second arrangement it may be necessary, in order to obtain acomplete coating, that the iron or alloy particles should be passedthrough the chamber twice; that is to say, the iron dust and magnesiumvapour are first admitted into the container in two impinging streamsand subsequently the partially coated dust is removed from the chamberand sent in again through the'nozzle 3 through which the irondustentered at the first treatment, a further supply of magnesium vapourbeing simultaneously admitted through its nozzle 4.

With the arrangement shown in Figure 1 the iron particles are placed inthe rumbler 1 which is rotated in the usual manner, for instance, bygearing 5, so as to carry the iron particles to the upper part of thechamber y means of the blades 6 and by this means throw the particlesinto the central part of the chamber. The magnesium vapour is projectedin a jet into this place by a spraying pistol 7 of known type and thevapour is by this means brought into close contact with the separateparticles of iron and a complete coating produced.

Somewhat similar procedures may be followed in the method of coating bymixin A rumbler may, for instance, be used but it is not necessary tosend in the powdered magnesium in the form of a jet. It may be placed inthe rumbler at the commencement of the operation with the magnetic dustand the two materials agitated together by the rotation of the rumbler.

When using the method in which .two streams of material impinge on eachother for powdered magnesium the procedure will be the same as thatdescribed for magnesium vapour.

The powdered materials ma be blown into the chambers by means of jets.of air or by other gas which is inert inthe sense that it does notproduce any disadvantageous chemical or physical effect upon thematerials.

If the coated dust is to be treatedbefore adhering to the iron dust.

In making up the powder for moulding, either before or after heattreatment, it may be advantageous to use a small quantity of binder, forinstance, up to about 8% of natural or synthetic resin, lac, gum orother suitable binding material. This binder is preferably applied bydissolving it in methylated spirit or other suitable solvent and mixingwith the dust, preferably in a masticator, so that all particles of thedust are completely and; uniformly coated. The solvent is driven offduring the mastication process, leaving a thin coating of the binder oneach separate particle. This method of mixing has been found to preventcaking;

The core is made up from the dustby pressing in a mould in known manner.

In the case of cores made up with coated iron dust, where the coatinghas not been heat treated before the application of the binder, the coreis now placed in a suitable container,

and the container, complete with core, is

placed in an autoclave and subjected to temperature and pressure by theadmission of steam. The time taken in this process will depend upon thesize and proportions of the core being dealt with.

What we claim as our invention and desire to secure by Letters Patentis 1. A magnetic core comprising compressed, powdered magnetic materialand separating material in which the separating material is magnesiumhydroxide.

2. A magnetic core comprising compressed,

finely divided magnetic material the particles of which are coated withmagnesium hydroxide. v

3. A process of manufacture of magnetic cores comprising applyingmagnesium to powdered magnetic material and subsequently treating themagnesium with steam at an appropriate temperature and pressure toconvert it into hydroxide.

4. A process of manufacture of magnetic cores comprising sprayingmagnesium va-' pour on to powdered magnetic material and subsequentlytreating this material. with steam at an appropriate temperature andpressure to convert the magnesium into magnesium hydroxide.

5. A process of manufacture of magnetic cores comprising the agitationof powdered magnetic material in contact with finely divided magnesium(vapour or powder) and subsequently treating the material with steam atan appropriate temperature and pressure to convert the magnesium intomagnesium hydroxide.

,6. A process of manufacturing magnetic cores comprising applying finelydivided magnesium to powdered magnetic material,

In testimony whereof we atfix our signatures.

SYDNEY BECKINSALE. HAROLD JOHN ALLCOOK.

